a) Field of the Invention
This invention relates to an apparatus for cooling water which is used to cool, for instance, a laser oscillator (hereinafter referred to as "a cooling apparatus", when applicable), and more particularly to a cooling apparatus in which cooling the cooling water with outside air is effectively utilized to greatly decrease the consumption of electric power.
b) Description of the Prior Art
An Ar laser or YAG laser oscillator is very low in energy efficiency. The electric power applied thereto is converted into laser beam at a rate of 10 to 30% at best, and the remaining electric power of 70 to 90% is consumed as heat. In order to remove the heat, a cooling apparatus is provided for the laser oscillator; that is, cooling water is circulated between the laser oscillator and the cooling apparatus to absorb the heat thus generated.
As typical examples of the cooling apparatus of this type, there are available an air cooling system using a refrigerator circuit wherein heat exchange is effected between cooling water and air through refrigerant, and a water cooling system wherein heat exchange is effected between primary cooling water and secondary cooling water. The term "refrigerator" as used herein is intended to mean the refrigerator which operates on a cooling cycle of refrigerant compression, heat-radiation, and expansion.
In the air cooling system using the refrigerator circuit, heat exchange is effected between a refrigerant cooled by the refrigerator and a laser cooling water (or primary cooling water), to cool the cooling water.
In the water cooling apparatus, the laser cooling water (or primary cooling water) is cooled with well water or secondary cooling water which has been cooled in the cooling tower.
FIG. 4 is a diagram showing the arrangement of a laser cooling apparatus of air cooling system which uses a refrigerator circuit.
The cooling apparatus 510, as shown in FIG. 4, comprises a refrigerating cooler 27, and a circulating pump 53, to supply cooling water to a laser power source 505 and a laser oscillator 2 in a circulation mode.
The refrigerating cooler 27 of the cooling apparatus 510 shown in FIG. 4 comprises: a compressor 33 for compressing refrigerant; a condenser 39 for condensing the refrigerant thus compressed; an automatic expansion valve 29 for expanding the refrigerant thus condensed; and a refrigerant - water heat exchanger 31.
The refrigerant (such as CFC and HFC) compressed by the compressor 33 is supplied to the condenser 39, where it is condensed by cooling. The condenser 39 is provided with a fan 37 which is adapted to blow the condenser 39 from outside thereby to remove the heat of condensation therefrom. The fan 37 is driven by a fan motor 35. As a result, the condenser 39 outputs liquified refrigerant. The liquified refrigerant thus outputted is sent to a drier filter 521, where water content is removed from the refrigerant. The refrigerant thus processed is sent to the automatic expansion valve 29, where it is expanded and gasified while being throttled. In this operation, the refrigerant is decreased in temperature by gasifying latent heat.
The refrigerant thus processed is supplied to the refrigerant - water heat exchanger 31, where heat exchange is effected between the refrigerant and the laser cooling water; that is, the latter is decreased in temperature. The refrigerant is allowed to come out of the heat exchanger 31, and is then compressed by the compressor 33 again. Thus, the above-described cooling cycle is repeatedly carried out to cool the laser cooling water.
On the other hand, when the circulating cooling water returns from the laser through a return pipe 11 to the cooling unit 510, and enters the refrigerant - water heat exchanger 31, where it is cooled. The refrigerant thus cooled is pressurized by a circulating pump 53. The refrigerant thus pressurized is sent through a flow-rate adjusting valve 65, a pressure meter 515, a temperature sensor 513, a flow meter 511, and a supply pipe 67 to the laser power source 505 and the laser oscillator 2. The cooling water is partially supplied through a bypass pipe 517 to a filter 519, where dust or foreign matter is removed from the cooling water. Further in FIG. 4, reference numeral 509 designates a temperature sensor; and 507, a flow sensor.
With the cooling apparatus shown in FIG. 4, in general the temperature of the cooling water is adjusted as follows:
(1) In the case where the heat load on the laser side is constant (for instance a rated output of 18 kW):
The temperature of the cooling water can be substantially stably set by heat-insulating the piping with the heat load of the cooling apparatus taken into account.
(2) In the case where the heat load on the laser side varies, or heat input or output other than from the laser side more or less affects the temperature of the cooling water, or outside air temperature affects the input and output balance with the heat load:
(a) The refrigerating compressor is turned on and off to adjust the temperature of the cooling water.
(b) For instance, an inverter is used to control the speed of the condenser's fan.
(c) A hot gap bypass circuit (not shown in FIG. 4) is provided between the inlet of the condenser and the outlet of the temperature expansion valve, so that when the temperature of the cooling water becomes lower than the predetermined value, a hot gas pipe valve is opened to adjust the temperature of the cooling water.
The above-described cooling apparatus of refrigerator type suffers from the following problems:
(1) A lot of electric power is consumed because the refrigerator (the compressor, and so forth) must be operated at all times during the operation of the cooling apparatus (and accordingly the laser oscillator) .
(2) In the case where the cooling apparatus is installed inside the room, it is necessary to provide a cooling air conditioner or ducts to remove the heat discharged from the cooling apparatus.
(3) In the case of the cooling apparatus which requires a cooling capacity corresponding to a high thermal load (for instance more than 10 kW), an additional construction (such as the construction of a foundation of 10 to 15 cm for outdoor installation of the overweight cooling apparatus) is required, which increases the initial equipment investment.
(4) The cooling apparatus is great in weight, large in dimension, large in noise, and great in vibration. Hence, the installation of the cooling apparatus is permitted only in factories, industrial areas, non-dwelling areas, and so forth.
(5) The rotary machines such as the compressor, the fan, and the pump make large noises and vibrate greatly.
FIG. 5 is a diagram showing the arrangement of a cooling apparatus 601 of water cooling apparatus.
The cooling unit 601, as shown in FIG. 5, comprises a water--water heat exchanger 611 as a cooler. Secondary cooling water (external cooling water) is supplied through a pipe 613 and a filter 614 to the heat exchanger 611, where heat exchange is effected between the secondary cooling water and the laser cooling water (or primary cooling water) which flows through a pipe 609, so that the laser cooling water is cooled. Examples of the secondary cooling water are circulating cooling water which is cooled in a cooling tower by evaporation, or underground water, or running water.
On the other hand, the laser cooling water is sent from the laser (not shown) through a return pipe 11 to a cooling water tank 45 in the cooling unit 601. The tank 45 is to standardize the variation in temperature of the cooling water returning from the laser. The laser cooling water is supplied from the tank 45 through a filter 605 and a pump 53 to the pipes 607 and 609. As was described before, the pipe 609 enters the heat exchanger 611. The pipe 607 bypasses the heat exchanger 611.
The cooling apparatus 601 includes a temperature control valve 617, which is adapted to control the flow rate of cooling water flowing in the pipe 607 relative to the cooling water flowing in the pipe 609, to thereby control the temperature of the cooling water at the outlet of the temperature control valve 617. The temperature of the cooling water at the outlet of the temperature control valve 617 is detected with a temperature sensor 619, which outputs a temperature detection signal. In response to the temperature detection signal, the temperature control valve 617 is controlled in a feed-back mode. The cooling water thus temperature-controlled is supplied through a flow control valve 65 and a supply pipe 67 to the laser oscillator.
The above-described cooling apparatus of water-cooling type suffers from the following difficulties:
(1) The amount of power consumed by the cooling apparatus of water-cooling type is relatively small (about 1/4 to 1/15 of the amount of power consumed by the cooling apparatus using the refrigerator circuit). However, the cooling apparatus uses a lot of running water, industrial water, or underground water as the secondary cooling water, so that it is considerably high in operating cost. On the other hand, sometimes during a dry season such as summer, the use of such water may be limited; that is, the operation of the laser may be limited.
(2) It is necessary to provide equipment (such as a cooling tower, a waste-water processing facility, pipes, and wells). If not available, they must be newly provided to operate the cooling apparatus; that is, in this case, too, the initial installation investment is relatively great (incidentally, in Japan, it takes at least 3,000,000 yen to dig a well).